1. Field of the Invention
The present invention relates to an optical fiber built-in type composite insulator which is used mainly in detection systems for finding out fault points at electric power transmission lines, electric power distribution lines, and transformer substations, etc., and a method of producing the same.
2. Related Art Statement
Heretofore, in order to automatically find out fault points in electric power supply systems, optical fiber built-in type composite insulators have been used which have a function to transmit signals from optical sensors provided at power supply source side to detectors provided at grounded side.
An example of conventional optical fiber built-in type composite insulators is shown in attached FIG. 5 wherein a structure of an optical fiber built-in type composite insulator having stacked and joined multi insulator bodies is shown. Referring to FIG. 5, an optical fiber 3 is inserted in penetration holes 2-1, 2-2 bored in the central axis portion of stacked insulator bodies 1-1, 1-2 which are connected to each other by flange type connector metallic fittings or flanges 8-2, 8-3. For airtightly sealing the inside of the insulator bodies 1-1, 1-2 from the exterior, the optical fiber 3 is fixed at the upper end of the penetration hole 2-1 and the lower end of the penetration hole 2-2, and silicone rubbers 5-1, 5-2 are arranged on the upper and lower ends as sealing stoppers for the upper and lower ends to form sealed portions, and silicone grease 4 is filled in the penetration bores 2-1 and 2-2. In addition, in order to improve airtight sealing of joined portion of the insulator bodies 1-1 and 1-2, a packing 12 made of a resilient material is arranged between the lower end of the insulator body 1-1 and the upper end of the insulator 1-2.
However, the above type optical fiber built-in type composite insulator has the following drawbacks:
(1) The silicone grease and ceramics constituting the insulator have a such large differences of thermal expansion coefficients from each other that an inner pressure is generated in the insulator when the insulator is heated and the sealing silicone rubbers forming the sealing portions of the insulators are liable to break down.
(2) The silicone grease is likely to leak out through the sealing silicone rubbers or the packing portion of the stacked insulators.
(3) The penetration bores of the stacked insulator bodies are occasionally so displaced in location from each other that the optical fiber is bent and can not be fixed in position.
Also, in the optical fiber built-in type composite insulators having stacked and joined multi insulator bodies, those having a flexible connector metallic fitting between the end surfaces of the opposing insulator bodies, those directly joining the end surfaces of the opposing insulator bodies tightly, and those directly joining the end surfaces of the opposing insulator bodies tightly and having connector metallic fittings arranged on the outer circumferential surfaces of the insulator bodies for clamping and fixing the joined end surfaces of the insulator bodies, have been known.
In such optical fiber built-in type composite insulators having stacked and joined multi insulator bodies, a sealing material filled between the connector metallic fittings and the outer circumferential surface of the insulator bodies, between the opposing end surfaces of the insulator bodies, or in the interior of the penetration bores, is deteriorated due to impregnation with moisture penetrated through the cement from the exterior, or the sealing material is impregnated with moisture and thermally expanded in the narrow gaps to destruct the insulator body when the temperature of the insulator is elevated.
Usually, in joining two insulator bodies, the insulator bodies each having a connector metallic fitting around the end of the outer circumferential surface thereof are joined at their opposing end surfaces, and sealed at their outer circumferential surfaces of the joined portion by a sealing member, and the joined portion is fixed and clamped by the connector metallic fittings with a cementing material therebetween. If the sealing is broken to permit rain drops, etc., to penetrate into the penetration bores through the opposing end surfaces of the insulator bodies, a leakage current is liable to flow along the penetration bores and short circuited trouble is likely to occur.
In addition, the joined state of the insulator bodies at the end surfaces can not be maintained for a long time by a mere fixing and clamping by means of the conventional connector metallic fittings, etc., so that joining strength of the joined portion is decreased with the elapse of time.
Moreover, when the connector metallic fittings are directly abutted to the opposing end surfaces of the insulator bodies, when the opposing end surfaces of the insulator bodies are directly abutted to each other, the opposing end surfaces of the insulator bodies can not sufficiently absorb large mechanical shocks which might occur therebetween, so that the opposing end surfaces are liable to conflict with each other and hence be destructed at the time of earthquake, etc.
Furthermore, when producing an optical fiber built-in type composite insulator having stacked and joined multi insulator bodies by stacking a multiple number of insulator bodies by means of connector metallic fittings, inserting an optical fiber in the penetration bores of the insulator bodies, and filling a silicone rubber in the penetration bores, all the assembling works have to be performed in a production plant, because the penetration bores are so small that the filling work has to be performed by an aspiration system. In addition, the insulator bodies have to be stacked before the work of inserting the optical fiber in the penetration bores, so that the production plant becomes to a large size, and the height of the stacked bodies can not be changed or varied, even if such change is required.